Preheat oven to 375°F
Grease insides of ramekins (from the 2oz piece) and swirl with sugar to coat.
Stack 2 pieces of chocolate in each ramekin.
Place on baking sheet for easy handling.
Melt remaining 4 oz (2 bars) chocolate with milk or water.
Whisk in egg yolks until smooth and glossy.
Place egg whites and cream of tartar in mixer bowl with whisk attachment. Whip at medium-high speed until foamy.
Gradually add sugar and continue whipping to form soft peaks.
Whisk 1/3 of the whites into chocolate mixture to lighten then gently fold into the remaining whites until almost uniform.
Divide evenly among ramekins, filling to cover chocolate pieces.
Bake about 12-15 minutes or until tops are puffed and crusty.